intro to xml

Intro to XML

Hachim HaddoutiAl Akhawayn University

SSE

[email protected]

http://mail.alakhawayn.ma/~H.Haddouti

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TOC

Intro W3C Historical () development Scenarios in XML and Data Management

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1) Motivation

XML - EXtensible Markup Language

Markup-Language

- mark up – Data and information about information within a document

in einem Dokument Developed thru World Wide Web Consortium (W3C) Well readable Mostl used as an exchange format

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W3C

(World Wide Web Consortium) Over 400 members: organisations, Hosted by MIT, INRIA,

Keio University, 50 full-time staff members Invention of WWW Examples:

– XML– HTML– DOM– XPath– XML Schema– ...

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Process at W3C

Note– Sugesstions(no responsibilty W3C)

Working Draft– Working in progress, work has to be approved by all

invloved in W3C Candidate Recommendation

– Approved for test implementation only Recommendation

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Phenomena XML

„XML is the ASCII of the 21th century.“ „XML is the ASCII of the Web“

Henry Thompson (1999)

Why popular ?

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What’s Wrong with HTML?

<DT><IMG SRC="greenball.gif" > <A NAME="object-fusion"></A>Y.Papakonstantinou, S.Abiteboul, H.Garcia-Molina. <A HREF="http://www-cse.ucsd.edu/~yannis/papers/fusion.ps">"ObjectFusion in Mediator Systems".</A> In <I>VLDB 96.</I></DT>

Y. Papakonstantinou, S. Abiteboul, H. Garcia-Molina.“Object Fusion in Mediator Systems”. In VLDB 96.

HTML is markup for presentation only

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...What’s Wrong with HTML...

<DT><IMG SRC= "greenball.gif" > <A NAME="object-fusion"></A>Y.Papakonstantinou, S.Abiteboul, H.Garcia-Molina. <A HREF="http://www-cse.ucsd.edu/~yannis/papers/fusion.ps">"ObjectFusion in Mediator Systems".</A> In <I>VLDB 96.</I></DT>

No Explicit Structure, Semantics, or Object-Orientation

Author

ConferenceTitle

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... And Some Repercussions

Lack of schema/semantics when querying the Web (HTML):

– "find documents (books, papers, ...)

where author = Michael Jackson" (... and learn how software engineering meets the moon walker ...)

– "create a list of M. Jackson's books and (if available) their prices"

=> HTML is inappropriate for

data exchange

automation of information management (retrieval, manipulation, integration)

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XML is ..

Standardized for all applications Exchange format worldwide (write once, read everywhere)

XML is a Meta language sprache in order to define other languages– examples: MathML, ChessML, XUL (User Interfaces),

CellML, Gene Expression Markup Language, Chemical Markup Language, XML/EDI, UN/EDIFACT

– Nowadays over 300

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So what is XML (all about)?

Executive Summary:• XML = HTML – idiosyncrasies (simplified syntax)

+ user-definable ("semantic") tags• Separation of data and its presentation• Tags such Font or CENTRE are not necessary in XML. XML uses struktured Tags,

such as TITLE, CHAPTER, etc. document structure remains constant over different media.

=> simple, very flexible data exchange format:

semistructured data model

=> new applications: • Information exchange (B2B), sharing (diglib), integration

("mediation"), archival, ...

• Web site management (XML+XSL stylesheets), ...

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…

It takes ten minutes to understand (base) XML, and then ten

month to understand the new technologies hung around it.

(Peter Chen)

So why XML course in AUI?

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Extensible Markup Language (XML)

De-facto standard adopted by W3C– Describes content rather than presentation

Three major differences to HTML– New tags may be defined at will– Nested structures– XML doc can contain optional description of its grammar

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Historical Development XML /1

from Neil Bradley: The XML companion

1997

1992

1960

1986

XML

HTML

SGML

WWW

InternetMarkup

Generalized

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Historical Development XML /2

W3C recomendations

Other proposals

In progress

1997

1998

2001

1999

2000

XPath 1.0

XQL XML-QL

Quilt

XUpdate

XMLSchema

XQuery 1.0XPath 2.0

XML

DOM

2002

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2) Documents ...

For communication between humans– Human – Human

• Natural (human) language Sprache is used, contains complex and irregular structures

For computer communication:– Computer – Computer

• Data-oriented – Human – Computer

• Document-oriented– XML allows representation and transport of this

information

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XML Documents

Bevor Syntax some examples of XML Documents

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Example: XML Document

<?xml version="1.0" encoding="UTF-8"?><invoice customerNo="k333063143">

<monthsprice>0,00</monathprice><detailedinvoice>

<call><date>26.2.</date><time>19:47</time><number>200xxxx</number><itemprice currency ="Euro">0,66</ itemprice>

</call><call>

<date>27.2.</date><time>19:06</time><number>200xxxx</number><itemprice currency ="Euro">0,46</ itemprice>

</call><call_charge_total currency "Euro">2.19</call_charge_total>

</ detailedinvoice></invoice>

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XML Document - Features

XML documents contain enthalten data and structure of data withing a document (self describing)

All documents have the same/similar structure (regular) Typed Information in XML documents

Fo the previous example: Information could be stored in DB.

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Other XML Documents

XML documents are also irregular

Semi structured information

document-centric information

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Recall semi structured data

Features of semi structured data Structure is irregular. Schema is implicitly included in data. Structure of data is incomplete. Schema is felxible. Schema is big. Schema is changing.

(Abiteboul, 1997)

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Object Exchange Model (OEM) /1

See slides of first session

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XML is Based on Markup

<bibliography>

<paper ID= "object-fusion"> <authors> <author>Y.Papakonstantinou</author> <author>S.Abiteboul</author> <author>H.Garcia-Molina</author> </authors> <fullPaper source="fusion"/> <title>Object Fusion in Mediator Systems</title> <booktitle>VLDB 96</booktitle> </paper>

</bibliography>

Markup indicates structure and semantics

Decoupled from presentation

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XML Elements

Structure in an XML document is provided by markup, which consists of elements

Element consists of start/end tags– Element can be empty

See naming rules for elements– XML processors are case-sensitive– Start with letter or underscore, avoid colon

Special element called ROOT element– Contains all other elements

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Element Content

XML element can be: empty OR have content ANY * OR be of mixed content-type (PCDATA I car I train I plane) OR have a list of child elements

*Elements with content type ANY are not checked by XML validators

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Sample Elements and their Content

ElementContentElement name

EmptyElement

Nested Element

<bibliography>

<paper ID="object-fusion"> <authors> <author>Y.Papakonstantinou</author> <author>S.Abiteboul</author> <author>H.Garcia-Molina</author> </authors> <fullPaper source="fusion"/> <title>Object Fusion in Mediator Systems</title> <booktitle>VLDB 96</booktitle> </paper>

</bibliography> Character Content (PCDATA)

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Markup and Character Data

XML docs are made up of markup and character data– You can reference EXTERNAL binary data with entity

references Markup: Start/end tags, entity references, character

references, comments, CDATA section delimiters, document type declarations, and processing instructions

Character data: all text that is NOT markup

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Example

<?xml version=“1.0” encoding=“UTF-8”?>

<DOCUMENT>

<GREETING>

This text is inside the <GREETING> element.

</GREETING>

<MESSAGE>

Welcome to the wild and woolly world of XML.

</MESSAGE>

</DOCUMENT>

general entity references

turns intoParsed Character Data

(PCDATA)

MarkupParsed character dataCharacter data

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XML Attributes

Be careful with the terminology vs. relational attributes Attributes defined as Name-value pairs

– Let you specify additional information in start and empty tags

Follow same naming rules as for tag names Attribute values are text

– Enclose in quotation marks (“ ”) Given attribute may only occur once within a tag, but

element can repeated. Special attribute types

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Element Attributes

<bibliography>

<paper ID="object-fusion"> <authors> <author>Y.Papakonstantinou</author> <author>S.Abiteboul</author> <author>H.Garcia-Molina</author> </authors> <fullPaper source="fusion"/> <title>Object Fusion in Mediator Systems</title> <booktitle>VLDB 96</booktitle> </paper>

</bibliography>

Attribute name Attribute Value

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Other XML Constructs

Prolog: XML Declaration, comments, processing instructions, DTD. XML Declaration

<?xml version = “1.0” standalone=“yes” encoding=“UTF-8”?> Comments

<!– this is a comment --> Processing Instruction

<?xml-stylesheet href=“book.css” type=“text/css”?> CDATA

– Escape block containing characters that are not to be parsed (o.w. would be recognized as markup), (Note with specifying DTD all attributes per definition are from type CDATA)

<![CDATA[<start>this is an incorrect element</end>]]>

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Other XML Constructs

Entities (like macros)– < for <

– > forr >

– & for &

– ' for ´

– " for “– Parameter entities in DTD’s

Document Type Definition– Defines the documents grammar– See separate lecture

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Well-Formed XML Documents

XML documents are subject to two specific constraints

– Well-formedness: A data object is an XML document if it is well-formed. A textual object is well-formed if:

• Document follows document production (prolog, root element, optional misc. part, e.g., comments and/or processing instrc.)

• Must adhere to the syntax rules specified in the XML 1.0 recommendation (eg. Unique attribute names, tags properly nested)

• Each parsed entity must itself be well-formed

– Validity: An XML document is valid, if it obeys the document type definition (DTD) or XML schema that you use to specify the legal syntax of the document

Ensures that XML document parses into labeled tree

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XML and Semistructured Data

<bibliography> <paper id=23...> <authors> <author>Yannis</author> <author>Serge</author> ... </authors> <title>Object Fusion</title> ... </paper></bibliography>

{bibliography: {paper: {

id: 23, authors: {author: “Yannis”, author: “Serge”, … }, title: “Object Fusion …”}}

}

XML Document

can be represented as ssd-expression

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XML = Labeled Ordered Graph

...

...

@id

23

bibliography

paper paper

authors

author author

Yannis Serge

titlefullpaper

Object Fusion …

XML denotes graphs with labels on nodes

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Ssd-expression = Labeled Unordered Graph

...

...

23

bibliography

paperpaper

authors

author

Yannis Serge

titlefullpaper

Object Fusion …

Ssd-expression denotes graphswith labels on edges

author

id

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XML Graphs

So far, only seen XML trees Using references, can create graphs

<state sid=“s2”>

<scode> NE </scode>

<sname> Nevada </sname>

</state> Can use IDREF attribute type, which holds the ID value of another element in

the document

<city cid=”c2”>

<ccode>CCN</ccode>

<cname>Carson City</cname>

<state-of state_ref=“s2”/>

</city>

ID: special attribute type; XML processorsmake sure that no two elements have the same value for the attribute that is of typeID in the same document.

IDREF: holds the ID value of anotherElement in the document.

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A Word About Order

Our semistructured data model is based on UNORDERED collections of tuples– As are relations– Unordered collections can be processed more efficiently

(exploited by commercial DBMS) XML is ORDERD

– Based on its origins in the information retrieval community

• Order is critical in documents– However, attributes in XML are UNORDERD

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Usage of Schema Description : DTD

Presentation, which elements can occur and how they will be nested

Also: Declaration of structure information

Advantages of DTD: – Similar to a documentation for XML Documents– Errors in XML documents could be detected– Better quality of XML Documents bcs structured and

well thought methodology

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Definition of Elements in DTD

XML Document:<speaker> Ronald Bourret </spaeker>

Corresponding DTD:<!ELEMENT spaeker (#PCDATA)>

XML document:<speaker>

<lname> Bourret </lname> <fname> Ronald </fname>

</speaker>

Corresponding DTD:<!ELEMENT speaker (lname, fname)><!ELEMENT lname (#PCDATA)><!ELEMENT fname (#PCDATA)>

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Definition of Elements in DTD cont.

Sequence (A , B)

A and B must occur in document in the given order

Alternative (A | B)

either A or B occurs in document Repetition

A? - 0..1 times

A+ - 1..n times

A* - 0..n times Mixed Content (#PCDATA | A | B)*

A, B or other text occurs in document

<!ELEMENT hotel (name, address)><!ELEMENT name (#PCDATA)><!ELEMENT address (zip, city, ((street, number ?) | BP))><!ELEMENT description (#PCDATA | equipment | gastronomy)*>

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Example: Definition of Elements

<!ELEMENT hotel (name, address)>

<hotel> <name>Hotel Anwal</name><address>...<address>

</hotel>

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Example: Definition of Elements cont.

<!ELEMENT address (zip, city, ((street, number?) | BP))>

<address><zip>53000</zip ><city>Ifrane</city >

<street> Abdelkrim El Khattabi</street><number>12<number>

<address>

<address>< zip > 62000 </zip ><city> Al Hoceima</city >

<bp>12345</bp><address>

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Example: Definition of Elements DTD cont.

<!ELEMENT description (# PCDATA | equipment | gastronomy)*>

<description> The hotel Anwal is located in front of the City Hall, with view to Atlas mountain, and high quality service.</ description >

<description > Our Hotel consists of <equipment> Sauna </equipment> und eine< equipment > swimming pool </equipment>.

The <gastronomy> Hotel restaurant</gastronomy> offers

regional cuisine and see foods. </ description >

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Attribute Syntax /1

Attribute will be assigned to each element of an XML document:

<spaeker tutorial=´T1´> Ronald Bourret </speaker>

Corresponding DTD:

<!ELEMENT speaker (#PCDATA)>

<!ATTLIST speaker tutorial CDATA #REQUIRED>

Start Tag EndTagElement content

Attribute name Attribute value

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Attribute Syntax / 2

XML Document

<coordinates x=´200´ y=´300´ z=´150´ />

DTD

<!ELEMENT coordinates (EMPTY)>

<!ATTLIST coordinates x CDATA #REQUIRED

y CDATA #REQUIRED

z CDATA #IMPLIED >

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Representation of XML Documents incl. elements and Attributes)

XML Documents are trees!

Example:<spaeker tutorial=´T1´>

<lname>Bourret</lname>

<fname>Ronald</fname>

</speaker>

Bourret

Element nodesText nodesAttribut nodes

T1

tutorial lname fname

Ronald

Speaker

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Declaration of Attributes in DTD

Attributes have A name A type (CDATA, ID, IDREF/IDREFs, ENTITY/ENTITYS, NMTOKEN/NMTOKENS or (value1|value2|...) predicates, whether the attribute

have to occur (#REQUIRED, #IMPLIED oder #FIXED) oder An optional default value (in case of #FIXED this is necessary)

<!ATTLIST price currency

CDATA #REQUIRED>

<!ATTLIST project id

ID #REQUIRED>

<!ATTLIST person project

IDREF #REQUIRED>

<!ATTLIST zip xml-sqltype

CDATA#FIXED ´INTEGER´>

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ID / IDREF

Attribute could also be defined as ID/ IDREF/ IDREFS

Values within a document are unique

<!ELEMENT project (title)>

<!ATTLIST project member IDREF

#REQUIRED>

<!ELEMENT person (EMPTY)>

<!ATTLIST person id ID

#REQUIRED>

...

<!ELEMENT department (EMPTY)>

<!ATTLIST department dep_id ID

#REQUIRED>

<project member=´p0001´>

<title>...</title>

</project>

<project member=´a0001´>

<title>...</title>

</project>

...

<person id=´p0001´>

<name> Khattabi</name>

</person>

...

<department dep_id=´a0001´>

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ID/IDREF-Overview

Values of IDREF Attributes show which IDs are referenced. These could of different element types.

Global uniquenesses of IDs is MUST. (compare to PK and FK in DB?)

Project

ProjectProject

title titlemember

dept

deptdept

Person personDep_iddept_id person

id id idperson person person

member

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Entities /1

General Entity Declaration:– Definition Document sections

<!ENTITY GermanDay ´ German Day September 30, 2003 ´ >

<!ENTITY Miteinander ´ Dialog of Culture ´>

<event>

We are glad to anounce you the organization of &GermanDay, entiteld &miteinander.

</event>

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Entities /2

Predefined Entities Special symbols

– < for <

– > for >

– & for &

– ' for ´

– " for “ Symbols could be not easily displayed bcs specific

processing is needed.

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Entities /3

Character Entities Decimal number in range 0..255

– Extended ASCII-set (ISO 8859/1), also called Latin-1 Decimal numbers in 256..65535

– Unicode (ISO 10646) Hexa decimal numbers, such x23 example:

– &#60 for <

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Entities /4

Non parsed Entities to incoporate other file formats– Pictures and others

Example:<!ELEMENT Hotel (#PCDATA)>

<!ATTLIST Hotel View ENTITY #IMPLIED>

<!ENTITY View_winter

SYSTEM „view_winter.gif" NDATA GIF>

<!NOTATION GIF SYSTEM 'gifviewer.exe'

<Hotel view=„view_winter">

Anwal Hotel

</Hotel>

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Entities /5

Parameter Entities– To be used in DTDs

example:– <!ENTITY % addressdef ´(city,zip,street,number)´>– <!ELEMENT address %addressdef;>

To be used as deklaration of DTD Objective: Resusage „Modularizing“

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A Complete Example



<!ELEMENT hotel (name, kategory?, address,

pathdescription, price*>

<!ATTLIST hotel id ID #REQUIRED

url CDATA #REQUIRED>

<!ELEMENT name (#PCDATA)>

<!ELEMENT kategory (#PCDATA)>

<!ELEMENT address (zip, city,

street, number, telefon,

fax?, e-mail?)>

<!ELEMENT zip (#PCDATA)>

...

<!ELEMENT pathdescription (#PCDATA)>

<!ELEMENT price (#PCDATA | singleroom |

doubleroom | appartment)*>

<!ATTLIST price currency CDATA #REQUIRED>

<!ELEMENT singleroom (#PCDATA)>...

<?xml version='1.0' encoding='UTF-8'?><!DOCTYPE hotel SYSTEM "hotel_dt.dtd"><hotel id="id001" url="http://www.anwal.ma"> <name> Hotel Anwal</name> <address> <plz> 53000</plz> <city>Ifrane</city> ... </address>

<pathdescription> The hotel Anwal is located in front of the City Hall, with view to Atlas mountain, and high quality service. </ pathdescription> <price currency =„DH"> <singleroom>from 200,-</></>...</hotel>

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Example of complete DTD

<!ELEMENT publications (book | article | conference)*>

<!ELEMENT book (front, body, references)>

<!ATTLIST book isbn CDATA #REQUIRED>

<!ELEMENT front (title, author+, edition?, publisher)>

<!ELEMENT title (#PCDATA)>

<!ELEMENT author (first, second, e-mail?)>

<!ELEMENT first (#PCDATA)>

...

<!ELEMENT edition (#PCDATA)>

<!ELEMENT publisher (#PCDATA)>

<!ELEMENT body (part+ | chapter+)>

<!ELEMENT part (ptitle, chapter+)>

<!ATTLIST part id ID #REQUIRED>

<!ELEMENT ptitle (#PCDATA)>

<!ELEMENT chapter (ctitle, section+)>

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Graphical Presentation of DTD

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Klassification of XML Documents

Data centric Documents

strukturec, regular

Examples: Product catalog, orders,

invoices

Document centric Documents

unstruktured, irregular

example: scietific article, books, emails

Websites

Semi structured documents

data and document centric

Examples: publications, Amazon

<order> <customer>Meyer</customer> <position> <isbn>1-234-56789-0</isbn> <number>2</number> <price currency=„Euro“>30.00</price> </position></order>

<content>XML builds on the principles of two existing languages, <emph>HTML</emph> and <emph>SGML</emph> to create a simple mechanism .. The generalized markup concept ..</content>

<book> <author>Neil Bradley</author> <title>XML companion</title> <isbn>1-234-56789-0</isbn> <content> XML builds on the principles of two existing languages, <emph>HTML</emph> and .. </content></book>

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Limitation of DTS

DTDs impose order Data Type instead of simple #PCDATA or #CDATA Lack of Range Specification

From DB point of view: we conclude that data typing offered by DTDs is inadequte.

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Recommendation

To get familiar with XML– Create an XML document including elements and

Attributes– Test wellformed– Create DTD– Test the validity

Use e.g. of XML Spy, www.xmlspy.com